1. Field of Invention
This invention relates to a projection display device which employs liquid crystal light valves as optical modulation devices to modulate illuminated light on the basis of an input image signal.
2. Description of Related Art
Projection display devices, employing liquid crystal light valves as optical modulation devices, have been proposed to project an image onto a projection screen. A liquid crystal light valve is constructed by a liquid crystal panel (liquid crystal cell) sandwiched between an incident-side polarizer and an emitting-side polarizer, which are set so that transmission axes of light are perpendicular to each other. The incident-side polarizer and the emitting-side polarizer are typically provided in the vicinity of an incident surface and an emitting surface of the liquid crystal panel. The liquid crystal light valve modulates polarized light (linearly polarized light) transmitted by the incident-light polarizer in response to a signal provided to the liquid crystal panel, and transmits only modulated light of the polarized light in the direction equal to that of the transmission axis of the emitting-side polarizer, thereby emitting the modulated light responsive to the given image signal.
FIGS. 6(A) and 6(B) each show a function of the polarizer. The drawings are provided with rectangular coordinates in which the direction of travel of light is referred to as the z direction, the horizontal direction is referred to as the x direction and the vertical direction is referred to as the y direction. FIG. 6(A) shows a state in which, when non-polarized light (for example, natural light) including s-polarized light (linearly polarized light of which the vibrating plane is the yz plane) and p-polarized light (linearly polarized light of which the vibration plane is the xz plane) is incident on a polarizer, in which the direction of the polarization axis is referred to as the y direction and the direction of the absorption axis is referred to as the x direction, only the s-polarized light in the direction equal to that of the transmission axis is emitted. That is, the polarizer usually transmits polarized light having a component in the direction equal to that of the transmission axis, and absorbs polarized light having a component in the direction equal to that of the absorption axis that is perpendicular to the transmission axis. Therefore, if the set transmission axis of the polarizer is shifted from the direction of the polarized light that is to be utilized, as shown in FIG. 6(B), the quantity of the polarized light utilized by being transmitted by the polarizer decreases, and the usage efficiency of the light deteriorates.
This invention solves the above problem of the conventional art devices, and its object is to provide a technique for setting a polarization direction of a polarization element accurately, and for preventing deterioration of usage efficiency of light and a reduction in image contrast.
In order to solve at least a part of the above problem, a first projection display device of the present invention includes:
an illumination optical system that emits illuminating light;
a light valve that modulates the illuminating light emitted from the illumination optical system on the basis of a given image;
a projection optical system that projects the modulated light emitted from the light valve;
a lens provided on a side of an incident surface of the light valve in order to illuminate an effective area of the light valve by utilizing the illuminating light emitted from the illumination optical system; and
a polarization element fixed on a flat surface of the lens,
wherein the lens is provided with a reference shape which is usable as a reference to position the polarization element.
A second projection display device of the present invention includes:
an illumination optical system that emits illuminating light;
a color light separation section that separates the illuminating light emitting from the illumination optical system into three color light;
three light valves that modulate the three color light on the basis of a given image;
three lenses that are each placed on a side of an incident surface of each of the light valves, in order to illuminate corresponding effective areas of the light valves by the three color light;
three polarization elements placed on a side of emitting surfaces of the three lenses;
a color light synthesizing section that synthesizes the modulated light emitted from the three light valves; and
a projection optical system that projects the synthesized light emitted from the color light synthesizing section,
wherein at least the polarization elements are fixed to flat surfaces of at least one of the three lenses, and
wherein the lenses to which the polarization elements are fixed are provided with a reference shape which is usable as a reference to position the polarization elements.
According to the first and second display devices, since the lenses to which the polarization elements are fixed are provided with a reference shape which is usable as a reference to position the polarization element, the polarization elements can be accurately positioned within the device. In addition, the lenses can be accurately placed. This can increase the usage efficiency of the polarized light emitted from the polarization element. In addition, if the positioning of polarization elements in the device is performed wherein the direction of transmission and the direction of absorption of light of the polarization elements is deviated, it causes a reduction in image contrast. According to the invention discussed above, the reduction in image contrast can be prevented.
In addition, in the second projection display device, a dichroic film may be formed between the flat surface of the lens to which the polarization elements are fixed and the polarization elements.
In this way, if the dichroic film is formed on the flat surface of the lens, a reduction in size of the device can be achieved as compared with a case in which a dichroic film is separately placed in the projection display device.
Additionally, the reference shape may include one or more planes provided on the end of the lens. The reference shape may also be a straight line drawn on the flat surface of the lens. In fact, any reference shape can be employed as long as it can be used as the reference for fixing the polarization elements to the lens.